Performance Based, Prescriptive Based and Objective Based codes?

[mtlogcabin]

i have heard lots of discussion on the pro's and con's of performance based versus prescriptive based codes but this was the first article I read on Objective Based codes?

I would like to hear other opinions especially from our Canadian and Australian building officials since them seem to have it within their codes.

Is it easier to navigate?

Does it provide consistency?

http://www.chba.ca/uploads/policy%20archive/2005/2000-09-01_02.pdf

 

[Builder Bob]

No consistency as fire modeling software is highly dependent upon judgmental input..... which is a mian source of providing documentation that the performance based design meets fire safety issues that are nor prescriptive by the code.

 

[jdfruit]

Interesting take on the concepts for codes compliance. Going from "if it's not in the code it's not allowed" to "prove it by the steps"

The legacy code orgs discussed and cussed the issue quite a bit but never got traction. Case studies from the Canadian and Australian experience will be quite interesting.

 

[tmurray]

It's good in the sense that it allows the local AHJ to use judgment in accepting alternate means to comply with the code, while not accepting liability for the proposal. Ultimately I am responsible for ensuring that the alternate solution has addressed the appropriate requirements of the code and ensuring that the proponent of the solution has the technical background to review the solution. Since the code is nice enough to tell me exactly what the intent of the section is, it really is a no brainer. at this point we have been ding it for 20 years...working good so far.

 

[tmurray]

No consistency as fire modeling software is highly dependent upon judgmental input..... which is a mian source of providing documentation that the performance based design meets fire safety issues that are nor prescriptive by the code.

I'm not sure I understand your comment. How could there be no consistency when the code tells you the metrics you have to meet and you have to use proven scientific concepts to get there?

 

[Builder Bob]

No consistency as fire modeling software is highly dependent upon judgmental input..... which is a mian source of providing documentation that the performance based design meets fire safety issues that are nor prescriptive by the code.

Same as truss or LVL designing software.....garbage in equals garbage out. Improper data entry or falsified inputs create false reports. The National Fire Academy had offered a two part class on Fire Modeling and how to dissect the data parameters to ensure accuracy of the fire modeling.

As it has been stated before by a design professional, I practice engineering as it is an evolving science.

 

[cda]

Sounds like the objective based code book is going to be

Twice as thick ????

 

[Sifu]

looks a little like some of the commentaries, may be able to enforce the intent as opposed to the strict letter............don't we all do that sometimes anyway????

 

[cda]

looks a little like some of the commentaries, may be able to enforce the intent as opposed to the strict letter............don't we all do that sometimes anyway????

Yep.........

And how to you explain a code that had been there for a hundred years

 

[jdfruit]

tmurray

How do you get a copy of the Canadian code intent document? Preferably free pdf.

Now I wonder if there could be traction for objective based codes in the US?

 

[tmurray]

tmurrayHow do you get a copy of the Canadian code intent document? Preferably free pdf.

Now I wonder if there could be traction for objective based codes in the US?

http://codes-guides.nrc.ca/IA/10NBC/intentframe.html''>http://codes-guides.nrc.ca/IA/10NBC/intentframe.html' rel="external nofollow">

http://codes-guides.nrc.ca/IA/10NBC/intentframe.html

Use the tree navigation system on the left hand side of the page. Our acceptable solutions part of the code is called Division B, which is broken into Parts.

Part 3 Fire safety, washroom requirements and accessibility (our version of ADA)

Part 4 Structural

Part 5 Environmental Separations

Part 6 HVAC

Part 7 Plumbing (sends you to National Plumbing Code)

Part 8 Safety at construction and demolition sites

Part 9 Housing and small buildings (includes offices, mercantile and low & medium hazard industrial up to ~6500 square feet & less than 4 stories in height)

For instance the following is the text that I get when I look up the requirement for a smoke alarm on each storey;

Objective OS1 Fire Safety

Attribution [F11-OS1.5]

Intent 1:

To limit the probability that a fire involving a storey will not be detected, which could lead to persons on that storey or on another storey not being promptly notified of the fire, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.

Intent 2:

To limit the probability that persons in sleeping rooms will not be promptly notified of a fire in other parts of the dwelling unit or within their room, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.

OS1 in general refers to provisions that are required for fire safety. We get a little more detailed when we look up F11 and OS1.5 together;

F11 refers to the following: To notify persons, in a timely manner, of the need to take action in an emergency.

OS1.5 refers to the following: persons being delayed in or impeded from moving to a safe place during a fire emergency.



So, someone could conceivably come up with a way to notify everyone there is a fire and make sure they are able to exit the building in a timely manner and prove that their method meets or exceeds the same level of safety that is achieved by the prescriptive code, it is acceptable as an alternative solution.

We have this for every single sentence in our code. I should note that this is not a consensus based code. Anyone can propose changes, they are reviewed for technical feasibility, and sent before a joint committee of industry experts, builders, and code officials for discussion. Then, the proposed code is released for a public review for comments. Once complete, the code is finalized and published during the next cycle. The main difference is the requirements for technical feasibility. Sprinklers in one and two family dwellings failed to meet this requirement (cost per life saved was too high).

 

[tmurray]

Same as truss or LVL designing software.....garbage in equals garbage out. Improper data entry or falsified inputs create false reports. The National Fire Academy had offered a two part class on Fire Modeling and how to dissect the data parameters to ensure accuracy of the fire modeling. As it has been stated before by a design professional, I practice engineering as it is an evolving science.

But that doesn't mean we don't allow trusses or LVL, we just make sure people have the right technical experience before we accept their proposal. Same with fire safety, I'm not going to accept a timed egress study from anyone but a fire engineer, just like I wouldn't accept structural plans from anyone but a civil engineer.

 

[tmurray]

Yep.........And how to you explain a code that had been there for a hundred years

if the question "why is this in the code?" does not fall within one of the objectives, you have one of two problems;

1. You need to add an objective as the requirement is technically sound, or

2. The requirement should be eliminated as there is no technical justification for its inclusion.

For instance our first version of an objective based code eliminated the requirement to have doors on bathrooms in single family dwellings. There was no technical reason for this other than market drive, so it was removed. This process took us 10 years.

 

[FM William Burns]

From the beginning of code development to present day even, prescriptive codes often had an emotional attachment versus empirical data (science) involved with the final outcome going into the book. It was not until I got involved with development that I was aware but only assumed the science was there. Performance based options were introduced in the NFPA process over 20 years ago and we were all waiting for the increased introductions to get where they are presently.

The standardization of prescriptive codes will never be successful since humans are the ones who are weighing on the interpretation and we factor in a blend of beliefs, emotion and science to reach a consensus and enter it into the latest and greatest edition of the code or standard. Personally, I welcome performance based or objective based theory since a building in your community may be structurally equal, but the means to protect it, evacuate it or service it may be drastically different.

We as professionals need to evaluate one’s abilities to live with a structure for (x) years and form a life and safety perspective this writer has to take into account available resources necessary to protect and serve it. For this reason PB/OB methodology can aid in those deliberations while considering approvals. One must evaluate all perspectives to sleep at night and that is just part of our service and obligations to our community.

It is also very true that junk science exists...... and junk in equals junk out. That is the investigator talking now..... all the more reason to minimize emotional beliefs when dealing with prescriptive code development. Sorry for the rant!

 

[jdfruit]

FM

Not a rant IMHO. Well thought, well measured, well said.

 

[cda]

if the question "why is this in the code?" does not fall within one of the objectives, you have one of two problems;1. You need to add an objective as the requirement is technically sound, or

2. The requirement should be eliminated as there is no technical justification for its inclusion.

For instance our first version of an objective based code eliminated the requirement to have doors on bathrooms in single family dwellings. There was no technical reason for this other than market drive, so it was removed. This process took us 10 years.

You mean I can take the door off my bathroom?? one less to paint!!!

 

[Mark K]

Many of the structural provisions are already performance based.

Since there are standards for wood I-joists and structural composite lumber in the NDS al,l the manufacturer needs to provide is evidence of compliance with the referenced standard. When this happens the building official is required to allow the use of the product as long as the design is consistent with the values determined by the standard.

The standards used must be based on objective criteria since the building official cannot add additional criteria to deal with any deficiencies in the standard. I would suggest that criteria in the Canadian code for exiting is not specific enough.